M o m e n t u m

Momentum is… Inertia in motion Mass x Velocity

Creating Momentum Greater Force = Greater Momentum Force creates acceleration, so pushing harder makes you go faster.

Impulse is… Force applied x Time applied Change in Momentum Therefore… Δ(mv) = Ft

Impulse is… Commonly confused with impact (be careful) The force applied Determined by solving the equation for force

Momentum Increasing Momentum: –Increase force or time –Greatest momentum: Big force for big time

Momentum Decreasing Momentum –When you stop you lose all of your momentum – impulse is same no matter how you stop –More time means less force (haystack) –Less time means more force (brick wall)

A Picture is Worth a Thousand Words Man moves back, increasing time and decreasing force Man leans in, decreasing time and increasing force

Bouncing When something bounces the impulse is greater because you bring velocity to 0 and then increase it the other way

Action Reaction Pairs…Again –Every action has an equal and opposite reaction –There are internal and external forces for every system –The parts of an action reaction pair can be any of the following: Both internal Both external One internal, one external

How does Action/Reaction relate to Momentum Forces that create movement must come from outside of the system Action/Reaction both within the system cancel out For movement one part of action/reaction pair must be within system and one outside.

Does Direction Matter?  Momentum is a vector quantity – it has direction. Because of this two momentums that are of equal magnitude and in opposite directions cancel each other out. *if there is no NET force or NET impulse acting on a system, the momentum of that system cannot change at all*

Law of Conservation The law of conservation of momentum says: in the absence of an external force, the momentum of a system remains unchanged.

Demonstration Watch the movement of the person at the front of the room as they throw the ball. –Was there movement of the ball? –Was there movement of the person –Is momentum conserved? –Is momentum a vector quantity?

A few more examples Conservation of momentum can also be shown with moving objects that undergo a weight change. –The following examples show a freight train that has weight added to it while it is moving – notice the change in velocity that occur with the weight increase Are mass and velocity proportional or inversely proportional?

Big Cart, Little Brick

Little Cart, Big Brick

The Fish Example Part #1

The Fish Example Part #2

Conservation in Collisions Net Momentum Before = Net Momentum After –Friction is usually considered to be negligible during the collision itself

Collision Types –Elastic collisions objects are not deformed or attached and don’t generate heat or sound. –Inelastic collisions colliding objects become tangled or coupled together. They still follow the law of conservation, but after the collision they are attached to each other.

Inelastic Collision Example #1 This demonstration illustrates an astronaut in a frictionless environment undergoing an inelastic collision with another astronaut

Inelastic Collision Example #2

Inelastic Collision Example #3

Inelastic Collision Example #4

Inelastic Collision Example #5

Elastic Collision Example #1

Elastic Collision Example #2

Elastic Collision Example #3

Look at the difference…

Momentum Vectors  Momentum vectors combine like all other vectors.  When looking at the vectors involved in a collision the vector(s) before and after the collision must have the same resultant.

Vector Collision Example